Building a data access layer

I recently agreed to help a student out with a software development assignment out for university. At first glance, it looks to be a pretty heavyweight peice of work for an undergrad to be given, even more so when the undergrad doesnt have a lot of experience in software development.

Essentially, the assignment is to create an Ebay-esque Windows Form app. The wording of the assignment makes it look harder than it actually is, when you get around the features that are being requested the actual technical requirement is really very simple. The assignment needs to be split into several peices, something that a lot of students probably wont be familiar with as it simply doesnt get taught at uni. The first section is the persistent data storage, I don't yet know what options are available at the moment, but the assignment spec asks for data to be retrieved from either a database or some XML. Now, I can understand why these features would be requested, it allows the application to be able to pick up its data from the local infrastructure or from a web service.

So, they key technical part here? Well, it's a data access layer. I have put together a few of these now, normally as part of an architectural migration to ease the switch over, all this assignment really needs is an appropriate DAL in order to get its data into the Windows app. It struck me that there really isnt a lot of info on how to do this rather simple thing, I think with the maturation of ORM like nHibernate and Linq-to-SQL a lot of people are over looking this for smaller projects. Anyway, I plan to put together a short howto on building your own DAL, because once you understand how the things work in the firs place, it makes implementing your own or using one of the ORM's already out there a lot more intuitive.

Old School Computing, in its most truest sense.

Recently, I posted about the excellent machines that a rejuvinated Acorn Computers are now selling on the Internet. It got me thinking, anyone who went through an English school suring the late 80's and early 90's should have at least some distant memory of these rather fine machines.

For those that don't know, Acorn was one of the UK's only computer builders, a lot of people wont even remember them these days, but the ones who do will no doubt have fond memories of the BBC Master and probably playing Chuckie Egg on it.

Acorn made computers from 1978 to 1998, when they finally succumbed to the dominance of the PC architeture. There is loads about them on Wikipedia: http://en.wikipedia.org/wiki/Acorn_Computers, there are loads of these machines about now, mainly because of the sheer amount that were installed in schools across the country for so long. The first ever computer I owned was an Acorn Electron back in the early 80's. My parents thought that it might improve my hand/eye coordination to play games on it!! I think what many people wont realise is the lasting and prominent impact Acorn Computers have had on our everyday lives. Not only did they build their own computers, but they made their own OS, architecture and hardware. Acorn are resposible for developing the ARM processor, a peice of hardware that pretty much everyone carries around in their pocket, powering their mobile phone. It would be a fair bet to make that there is also one in your set top box at home, powering Sky, Virgin Media or your freeview/sat tuner. It doesnt start and end there either, ARM processors powered another venerable computing device towards the end of the 90's, the PSION Series 5. This is a very notable device as it was the precursor to the S60 mobile phone platform, the OS that powered it was called EPOC and it pretty much turned into Symbian - now things should start to be recogniseable!

With that said, I have now in front of me an original Acorn A7000+ desktop computer from a school down in England. It should run, I have powered it on and got the desktop up and displayed on my monitor. I plan to rennovate this UK computing relic to get it back up and running properly. I remember schools were using these machines right up until 2001 in some parts of the UK, this one I have here is a clear indication as it comes with an all important ethernet adapter.

One of the notable things about these machines is that they don't really need hard drives, the entire OS and all its supporting applications are stored on ROM. When you want to upgrade the OS, you simply replace the ROMs with your new set. This isn't something we see at all these days in a desktop computer, unless you are running a setup with embedded Linux.

I recall from the last time I saw an Acorn machine in operation, that it had a fully functional web browser. So, my plan right now is to get this bad boy up and running and connected to the Internet so that I can try and do some simple things like email and facebook. The example I have here, an A7000+, has a hard drive installed, as well as a CD writer, so this means I will be able to install software to it if I need to. From what I can see from the boot up screen, this machine is running RISC OS 3.7. From what I can remember, this was the last main release of the OS prior to Acorns demise, however since then there have been three seperate releases of newer OS's. In a rather different move to the normal distributions of Windows and Linux etc that we see now, a new company was formed in 1999 to release RISC OS 4. Not long after this, a seperate company release a RISC OS 5 for a seperate line of devices, but as far as I can tell this version of the OS is only for machines made by a company called Castle. This confuses me a bit, as far as I can tell this version of the OS has never really been available seperately.

But, a further twist is this, a new OS has been recently released, RISC OS 6... I have no idea how much of a departure this will be from the RISC OS I know and love. One thing that is very notable about RISC OS is that it pretty much introduced the concept of the task bar (as far as I know). This is very familiar to Apple users and now, to Windows 7 users, its a feature that Acorn introduced in 1988 though... As soon as I get this one up and running, I will start to get some screen shots up and running.

Sorting Lists with Comparison in .Net

The other day, I made a post about invoking methods using reflection. One of the things I wanted to do in my code was get a list of the methods in a class and then run them. However, what I didnt mention was that I wanted the methods added to my list in an order. Sorting a list is easy if you are working with a list of strings or numbers. But the list I generated was a list of type MethodInfo - something that .Sort wouldnt work with.

So, to overcome this, I did the following:

sectionNames.Sort(delegate(MethodInfo m1, MethodInfo m2) { return m1.Name.CompareTo(m2.Name); });

And out pops a sorted list of type MethodInfo. Short, but sweet and also provides a nice little example of how lists of different types can be sorted.

Sick of my phone

I am totally sick of my phone just now. For the past five years I have been using Nokia phones, mainly S60 smartphones. However, over the last few years I have been getting more and more frustrated with the S60 OS. It sees to me that once Nokia gained control of Symbian (at least I think it did) things started getting bad.

At the present time, I use an N96 - when it wants to work. Recently, one of my friends at work got hold of the HTC Hero, a smartphone that uses Google's Android 1.5. As far as I am concerened, it out cools the iPhone. However, I dont know if I want to get another smartphone. Right now I am thinking about getting a normal phone and some form of Internet Tablet/PDA - ironically I am looking at getting a Nokia N810. My reasons for this? Well, out of the box it runs a Linux, but you can also install Android on it as well :).

PDF Generation with PDFJet

As mentioned previously, I have been working a lot on report generation. Where I work just now, we produce a lot of reports. A lot of them are produced manually and are very large. An ideal candidate for automation.

I need to produce them in a number of different formats, pdf is the first one I tackled. All of the reports I need to produce use tables, so I needed to find a .Net pdf library that had this functionality. I took a look at what was on offer, open source, closed source and commercial. I went for a lib called PDFJet. This is a fairly mature Java pdf library that has been ported over to .Net for C# http://www.pdfjet.com/. Its fairly cheap and whilst it lacks a lot of in depth examples, there are quite a few available on their website. The support is really good too - if you have a question, the guys are able to provide feedback very quickly.

It is very well featured, but I am basically using it to generate tables from datatables. I have been using it in earnest for about a week now, so I will try and post some examples of how it can be used here. There are two ways of creating a table with PDFJet, you can use a delimited text file holding the data you need or you can build a table programatically. Doing it in the code is quite tricky, to do this you need to build a list of lists of type cell - not as easy as it sounds... However, I am very impressed with this library and the things it can do.

Automatically invoke methods from a given class

Had an interesting problem at work this week. I have been working on a way to automatically generate a number of (lengthy) reports in a number of different formats. Each report has a number of sections that in turn hold a number of subsections. Each subsection holds either a chart or a table. Each report needs to be presented as either a pdf, a doc, an xls or a csv file. Some of the sections in each report are used in other reports.

I came round to designing each section as a class, in each class is a method that generates either a datatable to build a table from or a chart generated as an image. I wanted the generation of these datatables and images to be as generic as possible, the methods called provide the objects I needed but the way I call them needed to be as generic as I could get it. So, instead of putting together a method that calls all of these other methods I came up with the idea of building a list of all the methods I need to call in order to generate a report. To do this, I used reflection.

Firstly, I needed to get a list of all the method names I wanted to call.

List<MethodInfo> sectionNames = new List<MethodInfo>();
Sections s = new Sections(conn);
Type t = s.GetType();
MethodInfo[] mi = t.GetMethods();
foreach (MethodInfo method in mi)
{
sectionNames.Add(method);
}

In this example, Sections is the name of the class holding the methods I need to generate a report. It populates its datatables from a database, so the conn variable holds the connection string needed. There are a lot of sections in the report I was working on, so I split each section up as partial classes. Using GetMethods () on my class returns all of the available methods within that class. With that information, I simply create a list of type MethodInfo and add each element of the array I have created to the list. I dont really need to do this, but at some point I am going to want to sort the list, which is a little easier than sorting the array (from my perspective). I now have a list of all the method names available in my class. The next thing I do is get rid of some of the generic methods, like GetType(). I dont know if there is a cleaner way of doing this, so all I am doing right now is deleting a range from the list:

sectionNames.RemoveRange(8, 4);

Now I have almost everything I need. Next up, I need to invoke the method and capture its return. The first type of report I tackled was a pdf. The library I am using to create these pdf's uses delimited text files to create tables (it can be done programatically, but I havent mastered this yet). So, I need to create a dictionary holding the name of the text file I want to create and the name of the method to create it from. Now, I also mentioned that my report will also hold charts generated as images - so the dictionary I create needs to hold a string and an object, not a string and a datatable or any other type. It may not be the cleanest way to do it, but I can cast the object as a datatable later on, anyway...

Dictionary<string, Object> content = new Dictionary<string, Object>();

Thats my dictionary ready to go, I just need to populate it with filenames and object. This isnt as hard as it seems, because my list contains type MethodInfo I can use the Invoke method to call all of the methods in the list. Thats a bit of a mouthful really, so it is better to demonstrate:

foreach (MethodInfo method in sectionNames)
{
object obj = method.Invoke(s, null);
content.Add(method.Name + ".txt", obj);
}

I loop through each MethodInfo type in my list. I create an object called obj, this becomes the return from each of the methods I call using Invoke. Once called and invoked, I add the result to my dictionary, on success the dictionary contains a key value pair representing a string filename and an object. You can see in the example above that the filename is always a .txt - this is bad when it comes to images (I am not creating any just yet). But, this can be worked around by getting the type of the object etc. However, right now this is all I need to create my text files to use with my pdf generation. I simply loop through the dictionary creating a textfile from the contents of the object (which is a datatable dont forget), the string is the filename the text file is created with.

Its not very efficient just now, I need to manage the methods in the dictionary - I need to remove the generic ones prior to adding them and I need to sort them in order, both things I either do manually or not at all right now. But this is a nice little example of how methods can be gathered from a class and then dynamically invoked. The complete source for this example is as follows:

/// <summary>
/// Creates a Dictionary of strings and object representing the content we want to build
/// </summary>
/// <returns>a Dictionary of strings and objects holding the filename and the datatable</returns>
private Dictionary<string, Object> Contents()
{
List<MethodInfo> sectionNames = new List<MethodInfo>();
Sections s = new Sections(conn);
Type t = s.GetType();
MethodInfo[] mi = t.GetMethods();
foreach (MethodInfo method in mi)
{
sectionNames.Add(method);
}
sectionNames.RemoveRange(8, 4);
sectionNames.Sort();
Dictionary<string, Object> content = new Dictionary<string, Object>();
foreach (MethodInfo method in sectionNames)
{
object obj = method.Invoke(s, null);
Console.WriteLine(obj);
content.Add(method.Name + ".txt", obj);
}
return content;

I will also post the file creation method that works with this after the weekend as well as some bits and peices to do with the pdf library I am using. But hopefully this should be enough to get someone else on the right track if they are also considering such a soloution.

Old School Acorn Computing

Just been doing a bit of a browse for info on my vintage Acorn A7000+ desktop when I discovered that Acorn Computers are back in business. I was impressed, however a little dismayed to see that they dont use the classic RISC OS operating system any more, but instead plump for Vista, or other versions of Windows. Their site is here: http://www.acorncomputers.co.uk/index.htm, and to be honest the devices they are selling do seem to be quite attractive. They come complete with the old school Acorn logo all over them, which just adds to the appeal.

I think anyone who still has fond memories of using Acorn and BBC computers when they were at school will enjoy taking a look at the new series of products. Of course, anyone who is still hankering for a bit of RISC OS action can take a look at Ebay, you can pick up an A7000+ very cheaply these days, some even with a network adapter. Schools are literally chucking these things out with the rubbish nowadays, unfortunately they can't even give them way to charities etc. However, if you really want the latest iteration of RISC OS, currently at version 5, check out Castle's list of products here: http://www.iyonix.com/. Personally, I dont see the need to spend almost £800 on a computer like this, but if you really are an enthusiast you will snap one right up.